This invention relates generally to systems and methods for distinguishing a signal having a frequency of interest from noise and more particularly, to systems and methods for recovering a signal of interest from a complex signal.
Electric machines, such as motors, are used for a wide variety of applications including but not limited to closing or opening electric switches, and/or providing power to electrical appliances. A condition monitoring system may be used to evaluate the condition of an electric machine by monitoring pre-determined frequencies of interest associated with the machine. Monitoring the frequencies of interest with which such an electric machine operates facilitates accurately determining whether the machine is operating satisfactorily or malfunctioning.
At least some known condition monitoring systems sample a plurality of signals from the machines being monitored to determine the associated operating conditions and communicate these conditions to an operator. The signals collected may be complex signals composed of a plurality of components that includes a signal component containing a particular frequency of interest and a component containing noise. However, because the magnitude of the noise that may exist in a machine output signal, it may be difficult to isolate the component containing the frequency of interest. Moreover, in some instances, the component containing the frequency of interest may not be easily isolated from the noise component when such frequency of interest component is indistinguishable from the noise component.
To facilitate isolating the complex signal component containing the frequency of interest, at least some monitors use a filter to narrow a range of frequencies, from the sampled signals to a band of frequencies that includes the frequency of interest. After the operational frequency range is narrowed, the frequency of interest may then be detected from within the frequency band. However, when the complex signal component containing the frequency of interest is indistinguishable from the noise component, all spectrum peaks may represent frequencies of the noise rather than the frequency of interest. Arbitrarily selecting one of the spectrum peaks may produce random results with little assurance of isolating the frequency of interest. Thus, it may be difficult to distinguish the frequency of interest from within the frequency band.
To further facilitate isolating the signal component containing the frequency of interest of a machine, at least some monitors use at least one oscillator. The oscillator may be configured to facilitate improving a signal-to-noise ratio of an input complex signal by adjusting an oscillation frequency of the oscillator based on a pre-determined frequency of interest of the input complex signal. This process is sometimes referred to as frequency rectification.
At least some known oscillators include physical, analog devices that oscillate within a set of pre-defined parameters. For example, an oscillator may be configured to output a signal with a pre-defined amplitude or range of amplitudes at a pre-determined frequency or range of frequencies. More specifically, an oscillator may be configured to output a continuous signal with an amplitude that oscillates back and forth between two values for a pre-determined number of cycles in a pre-determined period of time. Alternatively, at least some known oscillators are configured as electronic computer simulations of physical, analog devices to generate output signals substantially similar to the physical, analog models they are based upon.
These oscillators may be configured such that they tend to oscillate in an undisturbed state with a substantially stable frequency until a perturbation is introduced. These oscillators may also be configured such that when a perturbation is introduced to the previously undisturbed oscillator, the oscillator may tend to migrate to an alternate, substantially stable state with characteristics that are similar to the characteristics of the perturbation. For example, such an oscillator may be configured such that it oscillates with an undisturbed oscillation frequency within an order of magnitude of a frequency of interest. When a complex input signal, with a frequency of interest and noise components as described above, is input to the oscillator, under certain conditions, the oscillator may shift its oscillation frequency to be substantially similar to that of the frequency of interest. The resultant output signal from the oscillator may be represented by a frequency spectrum that has a notable peak substantially close to the frequency of interest due to a reduction of the noise component amplitudes. The relative amplitude of the signal at the frequency of interest is therefore increased relative to the noise.
Upon completion of frequency rectification, frequency extraction may be used to generate a frequency of interest signal for further utilization in subsequent equipment condition monitoring.
When electronic computerized models of the aforementioned oscillators are configured to execute frequency rectification, the associated configurations use a set of algorithms that may consume a significant amount of computing resources and may provide an undesired delay in determining if equipment malfunctions exist.